Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $68.33   11.749%   $76.3581   $76.36   $76.35   $76.40  
  Purchase #2 $116.42   9.336%   $127.289   $127.29   $127.30   $127.30  
  Purchase #3 $151.61   12.284%   $170.2338   $170.23   $170.25   $170.20  
  Purchase #4 $108.66   6.864%   $116.1184   $116.12   $116.10   $116.10  
  Purchase #5 $113.25   3.714%   $117.4561   $117.46   $117.45   $117.50  
  Purchase #6 $245.80   9.709%   $269.6647   $269.66   $269.65   $269.70  
  Purchase #7 $175.77   10.292%   $193.8602   $193.86   $193.85   $193.90  
  7 purchase totals = $979.84       $1,070.9803   $1,070.98   $1,070.95   $1,071.10